Glass and methods of devitrifying same and making a capacitor therefrom



y 13, 1965 A. HERCZOG ETAL 3,195,030

' GLASS AND METHODS OF DEVITRIFYING' SAME AND MAKING A CAPACITOR THEREFROM 7 Sheets-Sheet 1 Filed June 26, 1964 -50 -25 O 25 5o 75 IOO |z5= :50 I75 TEN/ 5k Tl/RE C INVENTOM ANDREW flake-zoo 1 6ND JTANLEYJ. .57'00/05'7 4r TOR/YE) July 13, 1965 A .HERCZOG ETAL 3,195,030 GLASS AND METHODS OF DEVITRIFYING SAME AND MAKING A CAPACITOR THEREFROM Filed June 26, 1964 '7 Sheets-Sheet 3 FIRST MELT/NG- o THEE J! CRYSTAL P A 5 ANN. P7. f 5 FEPPOEIECTRIC cw): TAL P/IASE TEMPE/PA TUBE 'INVENTQRS 1% 3 ANDREW flz-veczoe my JrA/vLEYfi. Jraonrs? July 13, 1965 A. HERCZOG ETAL 3,195,030 GLASS AND METHODS OF DEVITRIFYING SAME AND MAKING A CAPACITOR THEREFROM Filed June 26, 1964 7 Sheets-Sheet 4 FIRST MELT/N6 V A ANN.PT OTHER CRYSTAL PHASE FERROIL z-"crR/c RYSTAL I HASE INVENTORS 800 I000 I200 v TEMPERATl/Pf "6 I A/ oee-w 64996206 QND Jun/45y 0. Grooms-Y l 0 IL BY y 13, 1965 A. HERCZOG ETAL 3,195,030

GLASS AND METHODS OF DEVITRIFYING SAME AND MAKING A CAPACITOR THEREFROM Filed June 26, 1964 7 Sheets-Sheet 5 F/RST MELT/N6 A j h LJ L f ANN- PT FFRROElECTR/C I CRYS 7'41- PHASE 500 600 700 800 900 I000 H00 I200 I30 I400 INVENTORS- o Amp/25w bskc-zoe TEN/ 594 70/35 6 nxvo Jramasrfi. JTOOKEY 147 roan 7 July 13, 1965 A. HERCZQG ETAL 3,195,030

GLASS AND METHODS OF DEVITRIFYING SAME AND MAKING A CAIFACITOR THEREFROM Filed June 26, 1964 '7 Sheets-Sheet 6 E E N Q n O 25 5 o 735MPA 4 7'l/RE C I o o O o 0 O o O Q Q O O Q Q U (ll m w w INVENTORS ANDREW AEeczoe Alva JTANLEYfl- JrooKEY 61214 f 6 ATTORNEY July 13, 1965 A. HERCZOG ETAL 3,195,030

GLASS AND METHODS OF DEVITRIFYING SAME AND MAKING A CAPACITOR THEREFROM Filed June 26, 1964 7 Sheets-Sheet 7 tric constant were substituted for the mica.

United States Patent 3,195,030 GLASS AND METHQDS 6F DEVITREFYENG dAME AND MAKING A CAPACETUR THEREFRGM Andrew Herczog, Painted Post, and Stanley D. Stooirey,

Corning, N.Y., assignors to Corning Glass Works,

Corning, N .Y., a corporation of New York Filed June 26, 1964, Ser. No. 378,468 32 Claims. (Cl. 317-253) This application is a continuation-in-part of our pending application Serial No. 30,413 filed May 18, 1960 which application in turn was a continuation-in-part ofSerial No. 824,428 filed July 1, 1959, both now abandoned.

This invention relates to the manufacture of ceramic bodies having high dielectric constants and other desirable dielectric properties.

One of the earliest methods for making electrical capacitors involved the vertical stacking of thin sheets of mica, mica being well-known in the art for its dielectric properties. Later, thin sheets of a glass possessing a high dielec- However, these products did not exhibit as high dielectric strengths as some crystalline compounds, the most prominent of these being barium titanate (BaTifl Considerable research, then, has been directed toward means for making sound bodies from these crystalline materials.

Heretofore, such bodies have usually been made by molding and shaping a batch to form a body comprising finely divided ferroelectric crystalline compounds having the desired dielectric properties, such as BaTiO and/or various niobates either alone or in mixture with other titanates or zirconates or stannates together with very small amounts of siliceous or argillaceous bonding materials, and sintering the body without melting or otherwise altering its ferroelectric crystalline components. While the prior products have good and desirable dielectric properties, new compositions having still better dielectric properities are constantly being sought. The prior process has from time to time been improved with benefit to the uniformity and homogeneity of the product and to the reductition or" its porosity and voids but perfection in such qualities has not yet been attained. The prior process as now practiced consumes considerable time for the control of homogeneity and particle size which requires repeated ball milling and fritting of the batch before it is molded and fired. The molded body requires firing at 1100- 1300 C. for its proper sintering and maturing, as a result of which only platinum or palladium electrodes can be applied to the body in the green or unfired state because the cheaper silver and copper electrodes will not withstand such high temperatures. Moreover, the prior process is not well adaptable to produce sheets as thin as are desirable for the fabrication of some types of laminated capacitors, comprising a large number of dielectric layers for obtaining high capacitance per unit volume.

Such bodies have also been produced by melting a batch of the ingredients and then cooling this melt to room temperature at a rate slowly enough to cause devitrification to occur. Another method involves the melting of the batch materials, maintaining this melt at such a temperature (generally at about the liquidus temperature) that crystallization will occur in the melt and then quenching the melt to room temperature. Still another modification contemplates the incomplete melting of the batch materials ice such that a melt is obtained wherein unmelted particles of very small size are present therein to act as nuclei for the growth of crystals as the melt is maintained at a specitied temperature. After the desired growth of crystals has occurred, the melt is quenched to room temperature. The crystallization resulting from these processes is very nonuniform in the size of the crystals and the dispersion thereof in the glassy matrix is non-homogeneous. Hence, the exceptional dielectric properties of the base materials cannot be utilized to the best advantage.

The primary object of this invention is to provide semicrystalline ceramic bodies, having high dielectric constant and other useful properties for electrical applications, which can easily be obtained in the form of very thin sheets or in other useful forms in the glassy state and processed to the finished products in the same shape at much lower temperatures than similar materials known from the prior art.

Another object is to provide high dielectric constant materials with better breakdown strength and/or insulation resistance than similar prior materials.

Still another object is to provide an improved method of making semicrystalline ceramic bodies of high dielectric constant which provides a very wide range of control of dielectric properties by variations of conditions of processing.

A further object is to provide new compositions suitable for the production of such bodies by such method and for obtaining a wide range of characteristics desired for various applications.

Another object is to provide a laminated capacitor comprising a semicrystalline ceramic dielectric made according to the invention.

Another object is to provide a new method for fabrication of a laminated capacitor comprising a semicrystalline ceramic dielectric.

To these and other ends the invention embodies among its features a semicrystalline ceramic body, a method of making the body, new compositions for making the body by said method, an article comprising the body, and a method of making such article, to be hereinafter more fully described and illustrated in the accompanying drawing in which:

FIG. 1 is a graphical representation showing the relation between temperature in C. and the dielectric constant (K) of semicrystalline bodies made in accordance with the invention illustrating the effect of fluorine when present in compositions containing BaTiO SiO and A1 0 PEG. 2 is a graphical representation similar to that of FIG. 1 but illustrating the effect of an additional stable oxide when present in the compositions. As used herein, the term stable oxide means an oxide of a metal or of a metalloid which can be combined in the molten glass composition of the invention and retained therein without substantial loss by decomposition and/or volatilization;

PEG. 3 is a graphical representation of a curve produced by the Differential Thermal Analysis or DTA of a glass composition consisting essentially of Rat), TiO SiO and A1 0 in accordance with the invention showing the approximate temperatures of the annealing point of the glass, the formation of the ferroelectric crystal phase therein and the melting of such phase as the temperature of the glass is progressively raised;

FIG. 4 is a graphical representation of a DTA curve similar to that of FIG. 3 but illustrating a glass composition consisting essentially of BaO, TiO B and Cat) and showing the approximate temperatures of the annealing point, crystal phase formation and melting of the glass;

FIG. 5 is a graphical representation of the DTA curve of a glass composition consisting essentially of Nb O Na O, CdO, and SiO and showing the approximate temperature of the annealing point, crystal phase formation and melting of the glass;

FIG. 6 is a graphical representation in which the relationship between dielectric constant and temperature of some of the semicrystalline bodies of this invention is shown by a series of curves; and

FIG. 7 is a sectional elevation of a capacitor showing its internal structure comprising alternate layers of an electrically conducting material and of a dielectric material made in accordance with the invention.

We have discovered that a ceramic body containing at least one ferroelectric crystalline phase and possessing a high dielectric constant, conventionally and hereinafter designated K, a low dissipation factor or loss tangent, L.T., and higher breakdown voltage and insulation resistance than the prior products, together with other desirable physical and electrical properties, can be made by the controlled crystallization by heat treatment of a glass body of desired size and shape, having constituent oxides capable of combing to form such a ferroelectric crystalline phase or phases.

As used herein, the expression semicrystalline ceramic body means a body composed of a multiplicity of uniform very fine-grained crystals substantially homegeneously dispersed in a glassy matrix and forming a major proportion thereof, said body being produced by melting a glassforming batch containing the proper ingredients, cooling the melt to a glass and simultaneously forming a shape of the desired configuration, and then heat treating this glass shape in a particular manner to cause crystals to develop in situ.

The new products, originating as they do from homogeneous glasses made from fluid melts, possess zero porosity, optimum homogeneity and uniform dispersal of the crystalline phase or phases in very small particle size, as a result of which their resistitives reach 10 ohm. cm. at temperatures up to 400 C., and their dielectric constants and breakdown voltages are unexpectedly higher than those of bodies having the same or substantially the same oxide compositions but compounded and sintered in accordance with prior practice. The temperature of its heat treatment has an extremely large effect on the value of K of a body so made and provides a convenient and useful means for its control.

Furthermore, the thermal expansion coefficients of the original glass and the semicrystalline product derived therefrom are, in some cases at least, so nearly alike in value that breaking stresses are not established in relatively thin bodies, such as sheets, which may also be locally heat treated and crystallized to form regions of different K values in various portions. In such cases, any change in volume of the semi-crystalline portion during its crystallization is allowed to take place by the relatively low viscosity of the surrounding glass which is characteristic of these glasses above their softening point and which permits volume readjustment.

As a rule, the glasses of this invention soften without crystallization at about 10-50 C. or more below the temperature at Which crystallization begins. This permits sealing one piece of the glass to another before crystallizing them and is highly advantageous for making intricate shapes by pulverizing the glass, molding it and sintering the molded body at its softening point before crystallizing it.

We have found that the ferroelectric compounds tend to form and crystallize before other phases at temperatures in the overall range from about 700-1100 C. and that because of low formation temperatures fewer defective or oxygen deficient crystals are formed by the new process than by the prior sintering process, which is of further benefit to the dielectric properties of the new product. Moreover, a wider variety of compositions is now possible and electrodes of silver and copper can be applied to the glass body and successfully fired With the body to the final semicrystalline state, since in this temperature range such metal electrodes are not adversely affected.

Ferroelectric compounds in general are divided into four classes of which the family of compounds called the oxygen-octahedra family, characterized by an octahedral arrangement of oxygen ions in the crystal lattice, includes the ceramic ferroelectrics referred to herein (Proceedings of I.R.E. volume 43, pp. 1738-4793, especially page 1740). The types of oxygen-octahedra ferroelectric compounds, crystallographically designated as perovskite, the most important group, pyrochlore and other types, and also mixtures thereof, are particularly suitable for the purpose of this invention.

Perovskite type ferroelectric compounds have the general oxide formula, A30 wherein A and B are ions of large and small radii respectively, the total value of their valences being 6, and individually amounting either to the respective values 3 and 3 as for example in LaGaO or to 2 and 4 as in BaTiO or to 1 and 5 as in NaNbO More generally A ions may be selected from the first, second and third groups of the periodic table and B ions from the second through fifth groups. Other types of the oxygen-octahedra ferroelectric compounds are exemplified by CdNb O and W0 Solid solubility is wide spread among ferroelectrics and structural oxygen deficiency or excess with respect to the octahedral configuration may be mutually compensated by proper choice of the constituents of solid solutions.

In its broadest embodiment the present invention includes a semicrystalline ceramic body comprising, on the oxide basis, 30-90 cationic mol percent of the constituent oxides of at least one oxygen-octahedra ferroelectric compound, at least 30 cationic mol percent of said body comprising said compound as a crystalline phase uniformly dispersed in another phase, said crystalline phase being crystallized in situ from a homogeneous glass having the same oxide composition as the body and including at least one glass forming oxide, such as SiO A1 0 B 0 P 0 and the like which can be cooled from the molten state to form a glass.

While the invention is of general applicability in the production of semicrystalline ceramic bodies containing ferroelectric compounds of the oxygen-octahedra family and mixtures thereof, bodies containing the perovskite type ferroelectric compounds especially BaTiO have particularly advantageous properties, and the invention will hereinafter be described, for the sake of brevity, but not by Way of limitation, with respect to such preferred bodies and to compositions and methods therefor. Accordingly, the following discussion is chiefly concerned with ferroelectric ceramic bodies in which the ferroelectric crystalline phase is BaTiO but the invention in its broader scope includes bodies in which the crystalline phase or phases may comprise one or more of the other ferroelectric compounds of the oxygen-octahedra family or solid solutions or mixtures thereof as will be seen from the compositions hereinafter set forth.

For the production of one group of ferroelectric ceramic bodies containing BaTiO it is desirable to include in the composition Si0 and A1 0 to promote glass formation. The addition of a small amount of fluorine tends to improve the dielectric properties of the semicrystalline prod net and the melting characteristics of the glass. We have found that the broadest range of such compositions, on the oxide basis in cationic mol percent, comprises 30-45% B-aO, 15-40% TiO 726% SiO 340% A the amount of A10 not differing from the amount of SiO by more than of the amount of SiO and 0.5 1.5% fluorine, the total 3210, TiO SiO AlO and fluorine being at least 90%. Preferably, the amount of BaO should be O-l00% in excess of the 1/ l stoichiometric equivalent of BaTiO based on the amount of TiO present, said excess preferably being higher the lower the amount of TiO Cationic mol percentages are used in the compositions set forth herein in order to avoid the inaccuracies which arise in the calculation on the presumptively oxide basis of mol percentages of compositions having an oxide containing two or more of a given cation. According to this method of designating relative proportions, any given oxide formula is expressed as having one metal atom as the cation. If individual elements are present in any of the compositions herein in presumptively fluoride form, the cationic mol percent of the element is still set forth on the oxide basis. The oxide components of such compositions total 100 cationic mol percent and the fluorine, calculated as F is indicated as being extra and is expressed in cationic mol percent of the total. Inasmuch as the amount of fluoride present is quite small, the error arising therefrom is negligible.

A narrower range of compositions falling within the above recited range, in which the presence of fluorine is optional, comprises, on the oxide basis in cationic mol percent, 30-40% BaO, 1540% TiO the amount of BaO being 0l00% in excess of the 1/ l stoichiometric equivalent of BaTiO based on the amount of TlOg present, said excess being higher the lower the amount of TiO 9.5 26% SiO and 725% A10 the amount of A10 not differing from the amount of Si0 by more than about of the amount of SiO the total BaO, TiO SiO and A10 being at least 90%.

The method of utilizing any one of the above-defined compositions in accordance with the invention comprises melting it, cooling it rapidly to form a glass and heat treating the glass by heating it preferably between 850 C. and 1150 C. for a time ranging from at least 1 hour at 850 C. or at least /2 minute at 1150 C. to crystallize the glass. While a minimum time of heating as stated is essential, longer times are not harmful but are economically undesirable. The ferroelectric crystalline phase resulting from such heat treatment is BaTiO the advantageous dielectric properties of which are well known.

The above recited ranges of the constituents BaO, TiO SiO Al 0 and F are critical for the purpose of this invention for the following reasons: Since the desired dielectric properties of the semicrystalline products depend primarily upon their contents of crystalline BaTiO any substantial departure from the above recited minimum and maximum limiting percentages of R210 and T iO will result in an undesirable lowering of the amount of crystallized BaTiO and of the dielectric constant. An excess of 3210, up to of the l/l stoichiometric equivalent of the amount of Ti0 present, is desirable for the optimum result and such excess is believed to prevent the formation of other titanium compounds, such as the titanosilicates of barium, which lack the beneficial properties of BaTiO Such excess should be higher the lower the amount of Ti0 in order to favor the formation of BaTiO and hinder the formation of undesired crystal phases.

Compositions containing a deficiency of Bart) or, in other words, excess of Ti0 produce some of the benefits of the invention and are within the broader scope thereof. In such case meltability and glass forming ability are maintained either by the excess TiO itself or by the presence of an additional oxide or oxides and/or glass forming oxide or oxides.

An excess of SiO or a deficiency of A10 above or below the stated limits likewise increases the tendency towards the undesirable formation of silicates and a consequent lowering of the value of K; but too small an amount of Si0 or too large an amount of A10 causes the molten composition spontaneously to devitrify regardless of the speed of cooling. So as to produce a satisfactory glass, the amount of A10 should not differ from the amount of Si0 by more than about the amount of SiO present.

While the presence of fluorine is optional when the amounts of both BaO and Ti0 are close to their maximum, it tends to promote the formation of BaTiO and to suppress the formation of less desirable crystalline compounds, particularly when the Ba() and TiO contents are high. Excessive amounts of fluorine, however, make the glass susceptible to reduction during melting which also causes deterioration of the dielectric properties.

The fluorine is introduced into the glass as a metal fluoride, preferably a fluoride of a metal of the first or second periodic groups, which are thermally more stable than other fluorides. On account of the variation in their molecular weights, the proportion of fluorine per se in such compound will vary depending upon the metal. For convenience, the compositions, hereinafter shown in cationic mol percent, recite the percentages of the fluorine and of the oxide of the respective metal separate-1y. On this basis the maximum amount of fluorine should not exceed about 1.5%.

To further illustrate the invention, compositions containing BaTiO as the ferroelectric compound, Si0 as the glass-forming oxide and A10 within the abovementioned ranges, which may be utilized in carrying out the invention, are shown in Table I in cationic mol percent on .the oxide basis as calculated from their batches, together with the time (hours) and temperature C.) of heat treatment and the dielectric constant (K) and the loss tangent (L.T.) in percent of the resulting ceramic body measured at 25 C.

Table I 44. a 31. 2 35. 7 37. 3 33. 4 36.6 35. 4 35.1 22. 5 23. 0 28.2 32.3 19. 7 35. 0 35. 2 35.1 15.0 21.4 10.5 14.9 21.7 13.2 9.0 10.7 16.2 23.3 17.2 13.7 23.7 13.9 17.2 as 0.3 0.5 1.3 0.5 0.0 0.5 0.0 0.6 1.4 1.1 2.4 1.3 1.5 1.3 1.3 1.3 97.0 35.0 20.0 17.0 69.6 4.0 3.4 2 2 3 3 2 2 2 2.5 1,000 1,000 925 925 925 1, 000 1, 075 015 240 200 320 1, 370 300 800 840 050 1.5 2.8 3.1 2.8 3.2 3.1 2.9 2.4

T able I .Continued Excess BaO, percent.

Excess TiOz, pcroent Hours 2 2 2 3 C 1, 075 1, 075 1,000 1, 075 1, 075 925 K 800 1, 340 1, 370 1, 220 1, 320 1, 350 L.T 3.6 3.0 2.9 3.2 2.5 2.3

The compositions of this invention are preferably melted for 1 to 8 hours or more at 1400 C. or higher, as may be necessary, to produce homogeneous melts in crucibles, pots or tanks depending upon the size of the melt. Since the viscosities of the resulting glasses generally are relatively low (on the order of 1 poise above 1400 C.) fining of the melts presents no problem and the use of fining agents in the batches is unnecessary. Melting preferably should be carried out under neutral or oxidizing conditions. Barium nitrate or other nitrate may be used, if desired, as an oxidizing agent. The use of reducing agents tends to depreciate the dielectric properties. BaCO is preferable as the source of BaO and has the advantage .that the evolved CO maintains an equilibrium with its dissociation products (CO and Q) which tends to stabilize the state of oxidation of the melt.

Insofar as we are aware, the present glasses and useful articles composed thereof have never before been made because such compositions crystallize spontaneously unless, as we have found, the proper composition is used and they are cooled from a temperature above the liquidus to about 700 C. or below Within a few seconds, say about 2-10 seconds. The rapidity of cooling limits, to some extent, the thickness of articles which can be produced from the molten state, but we have found it possible to press slabs up to about /1 in thickness which cool as glass and are amenable to the subsequent heat treatment process. We have found that in the molten state their viscosity is so low, on the order of 1 to 10 poises at 1350 1400" C., that they are particularly well adapted for centrifugal casting or for making thin sheet glass by rolling. Such thin glass sheets are particularly suitable for the dielectric lamin-ations of capacitors, such as is shown in FIG. 6, for which purpose the thin glass sheets may, in known manner, be interleaved with metal foil strips or filmed with an electrically conducting coating before being laminated. The glass laminations are then sealed together by being heated to about 700 C. under pressure to enclose the metal laminations as described in United States Patent No. 2,405,529 and the glass is thereafter converted to a semicrystalline state by the above described heat treatment.

Articles of substantial thickness also can be made of G the new glass by quenching it from the molten state, as by pouring it on a cold metal plate or into a cooling liquid or dropping it to form shot, then pulverizing it and molding the powdered glass, as by the method described in United States Patent No. 2,390,354. Since, as we have found, the glass can be heated to its softening point temperature without being crystallized, the shaped article is heated at such temperature to sinter it 7 to a massive body. By the above described heat treatment the shaped glass article can then be converted to a semicrystalline body having the desired dielectric properties.

In Table I, the base compositions of Examples 4, and 9 to 14 inclusive, are similar to each other and vary principally in their fluorine contents, composition 9 being free of fluorine and compositions 4, and 10 to 14 containg various metal fluorides. It will be seen that the introduction of fluorine into the glass causes a substantial increase in the dielectric constant values and a small decrease in the loss tangent. The variation of the dielectric constant at room temperature with the particular metal fluoride which is added, however, is small and not critical.

The curves of FIG. 1 illustrate generally the efiect of variation of the TiO content in compositions containing an excess of R210, and also the effect of the presence or absence of fluorine, on the dielectric constant versus temperature curve, of semicrystalline bodies of the above described compositions made by the method of the invention. Examples 2, 3, and 11 of Table 1, containing fluorine and 23.0, 28.2, and 32.4 cationic rnol percent of Ti respectively, are represented by curves 2, 3 and 11, while Example 9, which contains 31.8 cationic mol percent of Ti0 but no fluorine, is represented by curve 9. Small variations in heat treatment and/or the SiO /Al O ratio, BaO/Ti0 ratio, the fluorine content have insignificant influence on the curves. The Curie point, indicated by the maximum value of K, at about 120 C. is to be seen in each of curves 2, 3, and 11 and this is in agreement with known data on BaTiO per se. A large difference in dielectric constant and Curie point is exhibited by curve 9 as compared to curve 11 which indicates that fluorine, when present, promotes the formation of BaTiO during the heat treatment of the present glass compositions.

Compositions l and 16 of Table I contain an excess Of In composition 14 the fluorine was introduced as BaF of which the barium as B20 is included in the total BaO.

In FIG. 2 are shown the types of curves representing the effect on dielectric constant versus temperture caused by addition of stable oxides to a semicrystalline body having the composition of Example 11 of Table I. Similar effects are produced by the same oxides when added to the other compositions of Table I. The amount of such oxides should not exceed about 10 cationic mol percent and preferably should not exceed 4 cationic mol percent, either individually or collectively. Specifically, curve A represents the composition of Example 11 per se and curves B, C. D, E and F represent in comparison the same composition additionally containing such stable oxides as are recited by way of example in Table 11 in which are shown: The amount of the respective glass form ing oxide in cationic mol percent added to composition r11;

the corresponding dielectric constant (K) at C.; loss tangent (L.T.) at 25 C.; Curie point (C.P.) in C.; dielectric constant (K) at the Curie point; type of curve, A, B, C, D, E or F classified according to Curie point; and

fthe optimum amount of the added oxide, where determined; designated best" in the last column. K and LT. were measured at a frequency of 1 kilocycle.

Table II Cationic mol percent L.'I. Curve of oxide added K 25 C per cel C.P., C. K at C P type Remarks 3.6 LiO 1, 100 2. 5 120 1, 400 A 2.2 Be 1,200 3.0 110 1, 900 A 1.3 MgO. 1, 700 3.0 50 1, 900 0 Best. 2.9 OaO 850 3.1 120 1,770 A 1.6 SrO 1,150 2. 100 2,050 A-B 2.7 Z110 2, 350 O. 5 2, 450 D D0. 1.3 000---- 1, 500 3.1 105 2,280 A-B 0.8 Gaona 1, 230 3. 0 120 2,250 A 0.2 TlO1, l, 2. 9 120 1,850 A 1.0 YO1 1,140 3. 3 120 2,100 A 1.2 LAO1,5. 1, 420 3. 3 2, 300 A-B 0.9 CeOz 1, 340 3.0 90 1, 000 B 1.3 ZrO 1, 400 2. 8 80 1,600 B 1.0 G60z 1, 250 2. 9 2,200 A 1.3 SnOz 1, 700 2. 8 50 2, 100 0 Do. 1.4 Sb01 5 900 2. 7 90 1, 350 B 0.8 BiOLs 780 3. 4 150 1, 500 G 1.8 VO;; 5. 800 2. 9 1, 300 A 1.2 NbOg 1, 500 2.1 80 2, 100 B 0.4 TaOg 1,250 2. 3 120 1, 860 A 0.8 CrO1 820 2. 8 105 1, 000 A-B D0. 0.4: M003"- 1,250 2.8 120 2,000 A 0A UOz 1,050 2. 5 105 l, 600 A-B 1.0 M1101 1, 050 0. 6 65 1, 200 E D0. 0.6 Pool 5 1, 500 3.3 80 2, 100 B D0. 0.7 C0O 1, 600 2. 2 50 1, 750 0 D0. 1.1 NiO.-- 1,200 0.6 0 1, 230 F D0. 0.7 PbO 1,100 3.0 120 1,950 A 0.4 GuO 1, 300 2. 5 100 2, 350 11-3 Do.

In some-cases, variations in the Curie point by the various added oxides amount to no more than 20 C. and the percentage of the added oxide is not critical. Some of the added oxides, such as the oxides of Ca, B, Ga, P, As, Tl, Y, Ge, In, Ce, Zr, Sb, Nb, Fe, Cd, La, Sn, Zn, Bi, and Pb, improve the glass forming characteristics of the compositions and lower the temperature coeificient of dielectric constant of their final products and, therefore, larger amounts, up to 10% of such oxides may be added with advantage.

The addition of oxides of In, Ce, Zr, Sb, Nb, or Fe will lower the Curie point to about 80 C. as shown in Curve B of FIG. 2 which is characteristic of compositions containing these oxides.

A curve generally intermediate of Curves A and B, but not shown in FIG. 2, is produced by the addition of oxides of Sr, Cd, La, Cr, or Cu.

softening points and heat treatment temperature for any particular glass can readily be determined.

In such procedure the temperature of a small capsule containing a pulverized sample of the glass to be heat treated is slowly raised and by means of a thermocouple inserted in the powdered glass and having its EMF. opposed to that of a similar thermocouple inserted in an inert powder, such as A1 0 and similarly heated, together with an automatic temperature recorder, any endothermal and exothermal reactions occurring within the glass as its temperature increases are indicated on a con- Curve C illustrates the eifect of the addition of oxides neighborhood of 50 C.

As is shown in Curve D, the addition of ZnO produces Curie points in the neighborhood of room temperature and also lowers the loss tangent substantially.

A low loss tangent is also produced by the addition of oxides of Mn as shown in Curve E and by the addition of an oxide of Ni as shown in Curve F.

The addition of an oxide of Bi, as indicated in Table II, raises the Curie point, as shown in Curve G.

The temperatures at which the glasses hereinbefore and hereinafter disclosed must be heated in order to convert them into ferroelectric semicrystalline ceramic bodies vary with composition, being generally lower for compositions containing the glass-forming oxide B 0 or mixtures of B 0 and SiO or P 0 The proper heat treating temperature will vary also with the proportion of the ferroelectric crystalline phase desired, being higher the larger the desired amount of the ferroelectric phase or phases. It is, therefore, impossible to state a temperature or range of temperatures in degrees which is suitable and effective for all compositions. However, by means of the well known procedure called Dilterential Thermal Analysis or DTA (described in the book entitled Diffe-rential Thermal Analysis: Theory and Practice by W. J. Smothers, 1958) the approximate annealing and tinuous graph, the abscissa of which indicates increasing temperature. As long as there is no such reaction in the glass the differential is zero and the curve is a substantially straight horizontal line. When the annealing point of the glass is reached, the beginning of a dip in the curve appears, showing the beginning of an absorption of heat. The temperature at the bottom of such dip is the softening point of the glass. This dip occurs in the range from about 500 C. to about 700 C. for the present glasses. As the temperature is further increased and the endothermal reaction is completed, the curve returns to the horizontal and, at about 50-450 C. above said annealing point, an exothermal reaction occurs which produces a sudden pronounced peak in the curve and which, according to X-ray diilraction data, indicates the crystallization of the ferroelectric compound as the primary crystalline phase. The separation of other crystallizable phases, if any, is also indicated by their respective peaks following the first peak. Several hundred degrees above the temperature of the first peak there occurs a dip in the curve which represents the first melting of the crystalline phases. The useful range of heat treatment temperatures for the glasses of this invention in general lies between the temperature of the first DTA peak or crystallization of the ferroelectric crystalline phase and a temperature about 50 C. below the bottom of the first melting dip. The time required for such heat treatments ranges from at least one hour at the peak temperature of crystallization of the ferroelectric phase to at least /z minute at about 50 C. below the bottom of the first melting dip of the DTA curve of the corresponding glass.

FIG. 3 represents the DTA curve for composition 4 of Table I and is typical of compositions comprising BaO, TiO SiO and A1 0 From the curve it will be noted that the glass of composition 4 has an annealing point at about 670 C., the ferroelectric crystalline phase crystallizes at about 820 C., and the first melting occurs at about 1280" C. We have found that the broad overall range of temperatures which are suitable for the heat treatment of such glasses, and for any one of the glasses in general disclosed herein, extends from peak temperature of crystallization of the ferroelectric crystal phase to a temperature about 50 C. below the first melting dip as shown by the DTA curve of the respective glass; and that the optimum temperature in such range is midway between the peak of the ferroelectric crystal phase and the nadir of the first melting dip in the curve. For composition 4 it will be seen that such temperature range is about 820-1230 C. and the optimum for obtaining highest K value is -about 1050 C. For illustration, the approximate values of the annealing point, ferroelectric crystal phase, peak temperature and first melting dip of each of compositions 1-14 of Table I are set forth in C. in Table III.

While compositions containing at least one fer-roelectric compound, preferably BaTiO together with at least one glass forming oxide, preferably SiO and an additional oxide, preferably A1 0 are hereinbefore shown in the preferred compositions of Table I, we have found that compositions consisting of at least one ferroelectr-ic compound and at least one glass-forming oxide make good glasses which can be heat treated to produce desirable semicrystalline bodies in accordance with the invention. Such compositions are shown by way of example in Table IV in cationic mol percent together withthe respective values for K and LT. percent for the semicrystalline products resulting therefrom.

Table IV into compositions consisting of the oxide components BaTiO and a glass forming oxide. Examples of such compositions consisting of the oxide components of BaTiO and also one of the glass forming oxides, SiO A1 0 B 0 and P 0 and the added stable oxides are shown in Table V in cationic mol percent together with their respective value of K and LT. The compositions of Table V all result in glasses when their melts are cooled rapidly. Some of these compositions contain stoichiometric amounts of BaO and TiO and the cationic mol percentages in such cases are equal. When either BaO or TiO is in excess of the stoichiometric amount, as will appear from the respective percentages given, the percentage of such excess may be calculated by' the usual procedure, if desired. Compositions in which the glass forming oxide is B 0 were heat'treated for 2.5 hours at about 850 C. All other compositions of Table V were heat treated for 2.5 hours at about 1000 C.

Table V PO23 c. Excess BaO, percent. Excess Ti02, percent K L.T., percent I L.'I., percent re Table V.Continued K L.T., percent FIG. 4 represents the DTA curve for composition 33 of Table V which contains the oxide components of BaTiO and the glass forming oxide B 0 The temperatures of the respective dips and peaks of this curve are generally lower than the corresponding temperatures of the DTA curve of FIG. 3. From the curve it will be noted that glass composition 33 has approximately an annealing point at about 530 C., a ferroelectric crystalline phase formed at about 660 C., and a first melting dip at about 970 C. The overall range of temperatures which are suitable for the heat treatment of this glass is 660920 C. with an optimum at about 790 C.

The compositions of Table VI, shown in cationic mol percent, contain the oxide components of a variety of ferroelectric compounds including one or more of: titanate of barium or cadmium; niobate of sodium or potassium or strontium or cadmium or barium or lead; zirconate of cadmium or barium or lead; tantalate of sodium or cadmium; ferrlate of lead or lanthanum; germanate of iron; or oxide of tungsten, W0 Each of the glasses of Table VI, after being heat treated, will contain one or more of such high permittivity (designated Hi Perm) crystal phases; the most probable phases are indicated for the respective compositions. It is to be understood, however, that while it is possible that the semicrystalline product of each composition may contain all of the-high permittivity crystalline phases or solid solutions thereof vindicated therefor, we have not as yet succeeded in identifying all of them therein. On the other hand, the high dielectric constants give a clear indication of the presence of one or more of the ferroelectric phases shown in the table. The materials in the finished semicrystalline state generally exhibit hysteresis effects characteristic for ferroelectric materials.

Table VI Hi Perm. crystal phases Cd,5NbOa Cd N v5 bOa caribou"..- CdNbOa.s.

L.T., percent Hi Perm. crystal phases.

NaZroa:

Table VI.C-ontinued' 850. K 182. L.T.,percent 1.0 01 3.0.

Bazroa Pb NbO3. Hlperm.crystalphases {PbZrOa 1 b,5;N bO3 BaNbOa, Cdzrot PbMOW-m srNbo3.i.I.. PbNbjFeba.

PbNbOa.5

Hi perm. crystal phases Ba .pr o

BaNbO3.5

BaNbOs,a

LaFeOe FIG. 5 represents the DTA curve for composition 76 of Table VI which contains the oxide components of NaNbO and Cd NbO and the glass forming oxide SiO The relative positions of the peaks and dips of this curve are roughly similar to those of the DTA curve of FIG. 3. From the curve is will be noted that glass composition 76 has an annealing point at about 600 C., a term-electric crystalline phase at about 690 C. and a first melting dip at about 1170 C. The overall range of temperatures which are suitable for the heat treatment of this glass is 6901l20 C. with an optimum at about 905 C. About 2 hours heat treatment is required to produce maximum crystallization at the optimum heat treating temperature.

It is to be noted that composition 90 of Table VI contains the constituent oxides of the ferroelectric compounds BaTiO and NaNbO in a total amount of 86.4 cationic mol percent. The compositions of this invention preferably should not contaain more than about 90% of the constituent oxides of ferroelectric compounds, since a small amount of a glassy phase or matrix is desirable to impart mechanical strength to the semicrystalline body. On the other hand composition 5 of Table I contains a calculated total of only 39.4 cationic mol percent of BaTiO and has a K:300. Compositions having less than about cationic mol percent of total constituent oxides of one or more ferroelectric compounds have relatively low K values although they still possess good insulation resistance and relatively high breakdown voltage.

In general the compositions of this invention are charactcrized by unusually high insulation resistance and breakdown voltages amounting to up to 10 ohms at 400 C. (composition 11 of Table I) and up to 4x10 volts DC. per cm. or 2 -10 volts A.C. per cm. (an average of a great many compositions in the system BaOTiO SiO Al O respectively.

In the curves of FIG. 6, dielectric constant is represented as a function of temperature for the semicrystalline products of a number of the compositions of Table VI. The curves are designated by the numbers of the the respective compositions were heat treated to convert them to the semicrystalline state in accordance with the invention are also indicated thereon. As can be seen from the curves, a variety of rates of change of capacitance with temperature can be obtained with different compositions.

In FIG. 7 is shown a capacitor in exaggerated size comprising a thin layer of a semicrystalline dielectric 10, made in accordance with the invention, a thin strip or film of metal or other electrically conducting or semiconducting material 11 in close contact with the opposite faces of the layer 10 and leads 12 of ribbon or wire in firm electrical contact with the opposite edges of the conducting strips .11. An outside layer of semicrystalline dielectric 13 surrounds and encloses the conducting strips 11 and dielectric layer 10 and is fusion-sealed t0 the leads 12. It will be understood that this novel construction is possible only by the method of assembly wherein the dielectric layer 10 and outer enclosure 13, at the time of assembly, are glass which is subsequently softened and joined to leads 12 after which the glass is converted to the semicrystalline state by heat treatment as described above. It will be obvious that such a capacitor so made is not limited to a single pair of conducting strips 11 but may comprise a plurality of alternate conducting strips with individual leads appropriately oriented, each of such strips being insulated and surrounded by the interposed dielectric layers and the outer dielectric enclosure joined to and forming a part of the dielectric layers. Thus, in capacitors in which there are several electrically conducting layers, two of said layers being connected respectively to input and output terminals, the remaining electrically conducting layers each may be connected to one of said terminals to proon the oxide basis, 30-90 cationic mol percent of the con- 1 7 stituents of BaTiO and at least one glass-forming oxide selected from the class consisting of Si A1 0 B 0 and P 0 cooling the melt to form a glass body and heat treating the glass body by heating it at a temperature between the peak temperature of crystallization of the BEITiOg and about 50 C. below the bottom of the first melting dip of the DTA curve of the glass for a time ranging from at least one hour at the lower of said temperatures to at least one-halt minute at the higher of said temperatures to crystallize the BaTiO and cooling the body.

2. The method of making a semicrystalline ceramic body in accordance with claim 1 wherein the glass-froming oxide is SiO 3. The method of making a semicrystalline ceramic body in accordance with claim 1 wherein the glass-forming oxide is A1 0 4. The method of making a semicrystalline ceramic body in accordance with claim 1 wherein the glass-forming oxide is B 0 5. The method of making a semicrystalline ceramic body in accordance with claim 1 wherein the glass-forming oxide is P 0 6. The method of making a semicrystalline ceramic body which comprises melting a composition comprising, on the oxide basis, 30-90 cationic mol percent of BaTiO SiO and at least 3 cationic mol percent of a metal oxide selected from the group consisting of CuO, BeO, MgO, CdO, 310135, ZYOQ, G602, V025, Nb02'5, W03, TeO and C00, cooling the melt to form a glass body and heat treating the glass body by heating it at a temperature between the peak temperature of crystallization of the ferroelectric compound and about 50 C. below the bottom of the first melting dip of the DTA curve or" the glass for a time ranging from at least one hour at the lower of said temperatures to at least one-half minute at the higher of said temperatures to crsytalilze the BaTiO and cooling the body.

'7. The method of making a semicrystalline ceramic body which comprises melting a composition consisting essentially of, on the oxide basis, 30-90 cationic mol percent of the constituents of BaTiO 3-30 cationic mol percent of A and SiO cooling the melt to form a glass body and heat treating the glass body by heating it at a temperature between the peak temperature of crystallization of the ferroelectric compound and about 50 C. below the bottom of the first melting dip of the DTA curve of the glass for a time ranging from at least one hour at the lower of said temperatures to at least one-half minute at the higher of said temperatures to crystallize the BaTiO and cooling the body.

8. The method of making a semicrystalline ceramic body which comprises melting a composition consisting essentially of, on the oxide basis, -90 cationic mol percent of the constituents of BaTiO 3-30 cationic mol percent of Alf) up to 4 cationic mol percent of an oxide of a metal selected from the class consisting of Na, K, Be, Mg, Ca, Sr, Zn, Cd, Ga, in, Tl, Y, La, Ce, Zr, Ge, Sm, Sb, Bi, V, Nb, Ta, Cr, Mb, W, Te, U, Mn, Fe, Co, Ni, Pb, and Cu, and Si();, cooling the melt to form a glass body and heat treating the glass body by heating it at a temperature between the peak temperature of crystallization of the ferroelectric compound and about C. below the bottom of the first melting dip of the DTA curve of the glass for a time ranging from at least one hour at the lower of said temperatures to at least one-half minute at the higher of said temperatures to crystallize the BaTiO and cooling the body.

9. The method of making a semicrystalline ceramic body as defined in claim 7 in which the composition contains 0.5-1.5 cation mol percent of fluorine.

' 10. The method of making a semicrystalline ceramic body as defined in claim 4 in which the composition contains, in addition to the constituent oxides of BaTiO and B 0 at least 3 cation mol percent of a metal oxide selected from the class consisting of CuO, BeO, MgO, CaO,

i8 ZnO, SrO, CdO, A10 YO ZrO ThO CeO SnO PbO, V025, TaO SbO BiO M003, W03, T602, M11015, F6015, and C00.

11. The method of making a semicrystalline ceramic body as defined in claim 5 in which the composition contains, in addition to the constituents of BaTiO and P 0 at least 3 cationic mol percent of a metal oxide selected from the class consisting of CuO, CaO, SrO, CdO, Nb025 and TaO 12. The method of making a semicrystalline ceramic body which comprises melting a composition comprising, on the oxide basis, 30-90 cationic mol percent of the constituents of a ferroelectric niobate selected from the class Consisting Of NaNbO Cd NbOg, SI NbO Pb NbO and Ba NbO and at least one glass-forming oxide selected from the class consisting of SiO A1 0 B 0 and P 0 cooling the melt to form a glass body and heat-treating the glass body by heating it at a temperature between the peak temperature of crystallization of the niobate and about 50 C. below the bottom of the first melting dip of the DTA curve of the glass for a time ranging from at least one hour at the lower of said temperatures to at least one-half minute at the higher of said temperatures to crystallize the niobate, and cooling the body.

13. The method of making a semicrystalline ceramic body which comprises melting a composition comprising, on the oxide basis, 30-90 cationic mol percent of the constituents of a ferroelectric meta-niobate selected from the class consisting of CdNbO SrNbO BaNbO and PbNbO and at least one glass-forming oxide selected from the class consisting of SiO A1 0 B 0 and P 0 cooling the melt to form a glass body and heat-treating the glass body by heating it at a temperature between the peak temperature of crystallization of the meta-niobate and about 50 C. below the bottom of the first melting dip of the DTA curve of the glass for a time ranging from at least one hour below the said temperature to at least one-half minute at the higher of said temperatures to crystallize the meta-niobate and cooling the body.

14. The method of making a semicrystalline ceramic body which comprises melting a composition comprising, on the oxide basis, 30-90 cationic mol percent of the constituents of at least one ferroelectric zirconate selected from the class consisting of CdZrO BaZrO and PbZrO and at least one glass-forming oxide selected from the class consisting of SiO A1 0 B 0 and P 0 cooling the melt to form a glass body and heat-treating the glass body by heating it at a temperature between the peak temperature of crystallization of the zirconate and about 50 C. below the bottom of the first melting dip of the DTA curve of the glass for a time ranging from at least one hour at the lower of said temperatures to at least one-half minute at the higher of said temperatures to crystallize the zirconate, and cooling the body.

15. The method of making a semicrystalline ceramic body which comprises melting a composition comprising, on the oxide basis, 30-90 cationic mol percent of tungstic oxide and at least one glass-forming oxide selected from the class consisting of SiO A1 0 B 0 and P 0 cooling the melt to form a glass body and heat-treating the glass body by heating it at a temperature between the peak temperature of crystallization of the tungstic oxide and about 50 C. below the bottom of the DTA curve of the glass for a time ranging from at least one hour at the lower of said temperatures to at least one-half minute at the higher of said temperature to crystallize the tungstic oxide, and cooling the body.

16. The method of making a semicrystalline ceramic body, which includes melting a composition, which, on the oxide basis in cationic mol percent, comprises 30-45% BaO, 15-40% TiO the amount of BaO being 0l00% in excess of the 1/ 1 stoichiometric equivalent of BaTiO based on the amount of Ti0 present, 726% SiO 13-30% A10 the amount of A10 not differing from the amount of Si by more than about of the amount of SiO and 05-15% F, the total BaO, TiO SiO A and F being at least 90%, cooling it to form a glass body and heat-treating the body by heating it between 850 C. and 1150 C. for a time ranging from at least one hour at 850 C. to at least one-half minute at 1150 C. to crystallize the glass.

1'7. The method of making a semi-crystalline ceramic body which includes melting a composition, which, on the oxide basis in cationic mol percent, comprises -40% BaO, 15-40% TiO the mount of BaO being 0-100% in excess of the 1/1 stoichiometric equivalent of BaTiO based on the amount of TiO present, said excess preferably being higher the lower amount of TiO 95-26% SiO and 7-25% A10 the amount of A10 not diifering from the amount of SiO by'more than about of the amount of SiO the total BaO, TiO Si0 and A10 being at least 90%, cooling it to form a glass body and heat-treating the glass body by heating it between 850 and 1150 C. for a time ranging from at least one hour at 850 C. to at least one-half minute at 1150 C. to crystallize the glass.

18. A semicrystalline ceramic body comprising, on the oxide basis, 30-90 cationic mole percent of the constituents of BaTiO at least 30 cationic mole percent of the said body comprising said BaTiO as a crystalline phase uniformly dispersed in another phase, said crystalline phase being crystallized in situ in a homogeneous glass having the same oxide composition as the body and including at least one glass forming oxide selected from the class consisting of SiO A1 0, B 0 and P 0 19. A semicrystalline c ramic body comprising, on the oxide basis, 30-90 cationic mole percent of the constituents of a niobate selected from the class consisting of NaNbO KNbO CdjNbOg, Sr N'bO Pb 5NbO3 and Ba NbO at least 30 cationic mole percent of said body comprising at least one of said niobates as a crystalline phase uniformly dispersed in another phase, said crystalline phase being crystallized in situ in a homogeneous glass having the same oxide composition as the body and including at least one glass forming oxide selected from the class consisting of SiO A1 0 B 0 and P 0 20. A semicrystalline ceramic body comprising, on the oxide basis, 30-90 cationic mole percent of the constituents of a meta-niobate selected from the class consisting of CdNbO SrNbO BaNbO and PbNbO at least 30 cationic mole percent of said body comprising at least one of said meta-niobates as a crystalline phase uniformly dispersed in another phase, said crystalline phase being crystallized in situ in a homogeneous glass having the same oxide composition as the body and including at least one glass forming oxide selected from the class consisting of SiOg, A1203, B203 and P205.

21. A semicrystalline ceramic body comprising, on the oxide basis, 30-90 cationic mole percent of the constituents of zirconate selected from the class consisting of CdZrO BaZrO and PbZrO at least 30 cationic mole percent of said body comprising atleast one of said zirconates as a crystalline phase uniformly dispersed in another phase, said crystalline phase being crystallized in situ in a homogeneous glass having the same oxide composition as the body and including at least one glass forming oxide selected from the class consisting of SiO A1 0 B 0 and P205.

22. A semicrystalline ceramic body comprising, on the oxide basis, 30-90 cationic mole percent of the constituents of tungstic oxide, at least 30 cationic mole percent of the said body comprising said tungstic oxide as a crystalline phase uniformly dispersed in another phase, said crystalline phase being crystallized in situ in a homogeneous glass having the same oxide composition as the body and including at least one glass forming oxide selected from the class consisting of SiO A1 0 B 0 and P 0 23. A capacitor comprising a plurality of electrically conducting layers each separated by a semicrystalline 20 ceramic dielectric, input and output terminals respectively connected to two of said electrically conducting layers, the remaining electrically conducting layers each being connected to one of said terminals, the semicrystalline dielectric comprising a body as defined in claim 18.

24. A capacitor comprising a plurality of electrically conducting layers each separated by a semicrystalline ceramic dielectric, input and output terminals respectively connected to two of said electrically conducting layers, the remaining electrically conducting layers each being connected to one of said terminals, the semicrystalline dielectric comprising a body as defined in claim 19.

25. A capacitor comprising a plurality of electrically conducting layers each separated by a semicrystalline ceramic dielectric, input and output terminals respectively connected to two of said electrically conducting layers, the remaining electrically conducting layers each being connected to one of said terminals, the semicrystalline dielectric comprising a body as defined in claim 20.

26. A capacitor comprising aplurality of electrically conducting layers each separated by a semicrystalline ceramic dielectric, input and output terminals respectively connected to two of said electrically conducting layers, the remaining electrically conducting layers each being connected to one of said terminals, the semicrystalline dielectric comprising a body as defined in claim 21.

27. A capacitor comprising a plurality of electrically conducting layers each separated by a semicrystalline ceramic dielectric, input and output terminals respectively connected to two of said electrically conducting layers, the remaining electrically conducting layers each being connected to one of said terminals, the semicrystalline dielectric comprising a body as defined in claim 22.

28. The method of making a capacitor which comprises assembling alternate layers of an electrically conducting material and a sheet of glass comprising, on the oxide basis, 30-90 cationic mol percent of the constituent oxides of at least one oxygen-octahedra ferroelectric compound, and including at least one glass-forming oxide, at least one of said conducting layers being attached to one metal lead, and at least one other conducting layer being attached to a second metal lead, heating the assembly sufficiently above the softening point of the glass to soften it and fuse the edges of the glass laminations together and seal them to the leads and thereafter exposing the assembly to a temperature between the peak temperature of crystallizathe bottom of the first melting dip of the DTA curve of tion of the ferroelectric compound and about 50 C. below the glass for a time ranging from at least one hour at the lower of said temperatures to at least one-half minute at the higher of said temperatures to crystallize the ferroelectric compound, and cooling the assembly.

29. The method of making a capacitor which comprises assembling alternate layers of an electrically conducting material and a sheet of glass comprising, on the oxide basis, 30-90 cationic mol percent of the constituents of at least one oxygen-octahedra ferroelectric compound, and including at least one glass-forming oxide selected from the class consisting of SiO A1 0 B 0 and P 0 at least one of said conducting layers being attached to one metal lead, and at least one other conducting layer being attached to a second metal lead, heating the assembly sufficiently above the softening point of the glass to soften it and fuse the edges of the glass laminations and seal them to the leads and thereafter exposing the assembly to temperature between the peak temperature of crystallization of the ferroelectric compound and about 50 C. below the bottom of the first melting dip of the DTA curve of the glass for a time ranging from at least one hour at the lower of said temperatures to at least one-half minute at the higher of said temperatures to crystallize the ferroelectric compound, and cooling the assembly.

30. A glass which, on the oxide basis in cationic mol percent, comprises 30-45% BaO, 15-40% TiO 7-26% SiO 3-30% A10 the amount of A10 not differing 21 from the amount of SiO by more than of the amount of SiO and O.51.5% fluorine, the total BaO, T iO SiO A10 and F being at least 90%.

31. A glass which, on the oxide basis in cationic mol percent, comprises 30-45% BaO, 15-40% TiO the amount of 3210 being l00% in excess of the 1/1 stoichiometric equivalent of BaTiO based on the amount of Ti0 present, said excess preferably being higher the lower the amount of TiO 7-26% S102, 330% A the amount of A10 not differing from the amount of SiO by more than about of the amount of SiO and 0.5- 1.5% fluorine, the total BaO, Ti0 SiO T10 and F being at least 90%.

32. A glass which, on the oxide basis in cationic mol percent comprises 40% BaO, 15-40% TiO the amount of BaO being 0100% in excess of the 1/1 stoi- 22 chiometric equivalent of BaTiO based on the amount of TiO present, said excess preferably being higher the lower the amount of TiO 95-26% SiO and 725% A10 the amount of A10 not differing from the amount of S10 by more than about of the amount of S10 the total B210, TiO SiO and A10 being at least References Cited by the Examiner UNITED STATES PATENTS 2,563,307 8/51 Burnham et a1. 106-39 2,663,658 12/53 Schurecht 117-70 2,920,971 1/60 Stookey 106-39 2,956,219 10/60 Cianchi 317-258 3,000,745 9/61 Cianchi 10639 TOBIAS E. LEVOW, Primary Examiner. 

18. A SEMICRYSTALLINE CERAMIC BODY COMPRISING, ON THE OXIDE BASIS, 30-90 CATIONIC MOLE PERCENT OF THE CONSITUENTS OF BATIO3, AT LEAST 30 CATIONIC MOLE PERCENT OF THE SAID BODY COMPRISING SAID BATIO3 AS A CRYSTALLINE PHASE UNIFORMLY DISPERSED IN ANOTHER PHASE, SAID CRYSTALLINE PHASE BEING CRYSTALLIZED IN SITU IN A HOMOGENEOUS GLASS HAVING THE SAME OXIDE COMPOSITION AS THE BODY AND INCLUDING AT LEAST ONE GLASS FORMING OXIDE SELECTED FROM THE CLASS CONSISTING OF SIO2, AL2O, B2O3 AND P2O5.
 23. A CAPACITOR COMPRISING A PLURALITY OF ELECTRICALLY CONDUCTING LAYERS EACH SEPARATED BY A SEMICRYSTALLINE CERAMIC DIELECTRIC, INPUT AND OUTPUT TERMINALS RESPECTIVELY CONNECTED TO TWO OF SAID ELECTRICALLY CONDUCTING LAYERS, THE REMAINING ELECTRICALLY CONDUCTING EACH BEING CONNECTED TO ONE OF SAID TERMINALS, THE SEMICRYSTALLINE DIELECTRIC COMPRISING A BODY AS DEFINED IN CLAIM
 18. 